Forming tool and forming process for producing an overpressure predetermined breaking point in a battery cover

Description

[0001] The invention relates to a forming tool and a forming method for producing an overpressure predetermined breaking point in a battery cover for a battery cell housing.

[0002] EP 1 108 269 B1 discloses a battery cell housing comprising a battery cell body and a battery cover. A groove-shaped predetermined breaking point can be provided in the base of the battery cell body, at which the base tears open in the event of excess pressure in the battery cell housing. The groove-shaped predetermined breaking point is curved and does not extend completely closed in the circumferential direction, forming a type of hinge to which the cover area, which opens in the event of excess pressure and is delimited by the groove-shaped predetermined breaking point, remains connected.

[0003] JP 2004-111155 A describes a forming tool for producing a predetermined overpressure break point in a battery cover for a battery cell housing. The forming tool comprises a die and a punch. The die contains a forming recess with a recess base defined by two recess flanks. The punch has a punch part. The length of the punch part in one stroke direction corresponds to the depth of the forming recess. A notching tool may also be present for creating notches.

[0004] Further battery housings are known, for example, from WO 2014 / 040676 A1 and DE 698 29 711 T2. These have a V-shaped groove in the battery housing, which is closed in a ring shape.

[0005] DE 10 2013 220 957 A1 describes a battery and a method for securing the battery. The battery has a battery housing that may include a pressure relief valve, a pressure equalization element, and a temperature control device, such as a cooling device.

[0006] US 2016 / 0296990 A1 describes a press for producing a metal membrane for a sensor in the automotive sector. The press has a die and a punch. The die contains a forming cavity. A punch part is arranged on the punch, the length of which is equal to the depth of the forming cavity.

[0007] BS & B GmbH offers reverse acting rupture discs that release pressure when a certain pressure threshold is reached (article "Controlled Pressure Relief", Industrieanzeiger 25.18, pages 52 and 53 and www.bsbsystems.de / Berstscheiben / explosionsschutz berstschei ben.html ) .

[0008] DE 22 30 333 C3 describes a metal can for pressurized liquids or gases with an inwardly curved base. This base features a circular perforation around the axis of the metal can, with individual incisions spaced at intervals along the circular path.

[0009] Based on the prior art, it is an object of the present invention to efficiently design the formation of an overpressure predetermined breaking point in a battery cover for a battery cell housing.

[0010] This object is achieved by a forming tool having the features of patent claim 1 and a forming method having the features of patent claim 5.

[0011] The forming tool according to the invention is designed to produce a predetermined overpressure breaking point in a battery cover for a battery cell housing. It comprises a die tool and a punch tool, which interact to produce the predetermined overpressure breaking point in the battery cover by forming.

[0012] The die tool has a support surface and a forming recess located in the support surface. The support surface is designed for supporting the battery cover to be formed. The forming recess extends completely or partially around an axis A. Preferably, the forming recess is completely closed in a circumferential direction around the axis A and is thus annular. The forming recess has a recess base. Viewed in an axial direction parallel to the axis, the distance between the support surface and the recess base defines a first depth.

[0013] An inner flank adjoins the base of the depression on one inner side and an outer flank adjoins the base of the depression on the opposite outer side. The inner flank of the depression is arranged closer to the axis than the outer flank. The forming depression preferably has a groove-like shape. It is open on the side opposite the base of the depression. In cross-section, the forming depression can be U-shaped, whereby the inner flank of the depression and the outer flank can run parallel to one another. Alternatively, it is also possible for the distance between the inner flank of the depression and the outer flank of the depression, viewed at right angles to the axial direction, to also increase with increasing distance from the base of the depression. The width of the forming depression can thus increase in the axial direction away from the base of the depression.

[0014] The punch tool has a punch part on its side facing the die tool. The punch part is preferably completely closed in a ring shape if the forming depression is also completely closed in a ring shape. Otherwise, the punch part can extend only partially around the axis A, analogous to the forming depression. The punch part extends in the axial direction, starting from a punch base surface to a free end. The free end faces the die tool. The distance between the free end of the punch part and the punch base surface in the axial direction defines a second depth. The second depth is greater than the first depth. Viewed in the axial direction, the punch part is positioned above the depression base. For example, the inner flank of the depression and the outer flank of the depression can define a hollow cylindrical space around the axis A, with the punch part located within this hollow cylindrical space.The outer surface of this hollow cylindrical space extends through the outer flank of the recess, and the inner surface of this hollow cylindrical space extends through the inner flank of the recess. The two surfaces are aligned parallel to each other.

[0015] The cross-section of the stamp part determines the cross-sectional shape of a bead to be formed into the battery cover for the overpressure breaking point.

[0016] When forming the battery cover, the forming tool allows a material flow between the punch tool and the die tool into the forming recess, the volume of which corresponds at least to the volume of the formed bead. The volume of the forming recess is preferably larger than the volume of the formed bead. Below the bead, a wall thickness of the battery cover remains, at which the battery cover can break or tear open when a pressure threshold is reached. The defined material flow when forming the battery cover into the forming recess can control or determine the material hardening. In addition to the remaining wall thickness of the battery cover at the overpressure predetermined breaking point, the material hardening during forming influences the pressure threshold at which the battery cover tears or breaks open.The forming tool according to the invention allows a repeatable, precise forming of the battery cover in order to obtain an overpressure predetermined breaking point in the battery cover, which triggers at a defined pressure threshold value.

[0017] The shortest distance between the inner flank of the recess and the outer flank of the recess perpendicular to the axial direction defines a first width. The volume of the forming recess, which is preferably larger than the formed volume of the bead, can be achieved by selecting a correspondingly large first width.

[0018] The punch part has an annular part inner surface extending between the free end and the punch base surface, and an annular part outer surface extending between the free end and the punch base surface. The annular part inner surface and the annular part outer surface are arranged at a distance from each other at right angles to the axial direction. The maximum distance between the annular part inner surface and the annular part outer surface defines a second width.

[0019] The inner surface of the ring part and the outer surface of the ring part can be aligned parallel to each other or inclined to each other. Starting from the free end, the width of the punch part can also increase with increasing axial distance in the axial direction. The punch part can thus have an increasing width starting from the free end toward the punch base surface.

[0020] The first width is at least a factor of 2 greater than the second width and in particular at least a factor of 3 or 4 or 5 greater than the second width.

[0021] In a preferred embodiment, the forming tool has, in addition to the die tool and the punch tool, a hold-down assembly with at least one hold-down device. The at least one hold-down device of the hold-down assembly lies opposite the die tool and is arranged adjacent to the punch tool. In one embodiment, an inner hold-down device and an outer hold-down device can be present, wherein the punch tool is arranged at right angles to the axial direction between the inner hold-down device and the outer hold-down device. The inner hold-down device can thus protrude into the annular punch tool. The outer hold-down device can enclose the punch tool in a ring-shaped manner. The at least one hold-down device can be resiliently mounted on the punch tool in the axial direction, such that the at least one hold-down device can be moved in the axial direction via the drive of the punch tool.Alternatively, at least one of the existing hold-down devices, for example, the inner hold-down device, can be arranged immovably relative to the punch tool, for example, even formed integrally with the punch tool. It is also possible to move the at least one hold-down device in the axial direction via an additional drive.

[0022] In particular, using the previously described forming tool, a forming process for producing the overpressure breaking point in the battery cover can be carried out. For this purpose, the battery cover is first placed on the support surface of the die tool and thus between the die tool and the punch tool. The die tool and / or the punch tool are then moved towards each other in the axial direction, whereby the punch part is pressed into the battery cover. Material flows into the forming recess of the die tool and an upwardly open bead is created in the battery cover. Below the bead, an area of ​​the battery cover remains with a wall thickness that is thinner than at other points on the battery cover, thus forming the overpressure breaking point.

[0023] During the forming process, a clamping force can be generated between a blank holder assembly and the support surface of the die tool before or simultaneously with the pressing of the punch tool into the battery cover. This prevents accidental, undesired deformation of the battery cover during the forming of the bead and supports the flow of material from the area of ​​the battery cover into which the bead is being formed into the forming recess.

[0024] In a preferred embodiment of the forming tool, the base of the depression is substantially flat and can, in particular, extend in a plane oriented perpendicular to the axial direction. Alternatively, the base of the forming depression can also have one or more elevations, in particular annular elevations. The annular elevations can extend in the circumferential direction around the axis.

[0025] After forming the bead, at least one additional notch is formed into the battery cover within the bead using a notching tool. The remaining wall thickness in the area of ​​the bead base can be at its smallest directly adjacent to or directly below the notch. By creating at least one notch after forming the bead, the remaining wall thickness on the battery cover adjacent to the notch can be very precisely adjusted. This allows the pressure at which the cover breaks or bursts to be defined very precisely, preferably with a tolerance of no more than 1-2 bar.

[0026] In a preferred embodiment, the notch tapers from the bead into the battery cover. In cross-section, the notch can have a V-shaped or triangular shape.

[0027] The at least one notch is not completely closed in the direction in which the bead extends in the battery cover, viewed in plan view of the top side of the battery cover. Preferably, the at least one notch extends only along a section along the bead. If multiple notches are present, they are arranged at a distance from one another. For example, it is possible to provide a notch at least in one region of the bead in which the bead runs in a curve as viewed in plan view of the top side of the battery cover. It is also possible to provide a notch in all regions in which the bead runs in a curve as viewed in plan view of the top side of the battery cover. A common notch can also be assigned to multiple curved sections of the bead.

[0028] The notch is preferably located at a point within the bead where the bead base transitions into a bead flank through a radius or a curvature. In particular, the notch is present in the transition area between the bead base and the bead flank, which is closer to the axis and thus, so to speak, located inside the bead. The notch can also be located in the transition area between the bead base and the bead flank, which is located further away from the axis and thus, so to speak, outside the bead.

[0029] Advantageous embodiments of the invention will become apparent from the dependent patent claims, the description, and the drawings. Exemplary embodiments of the invention are explained in detail below with reference to the accompanying drawings. They show: Figure 1 a schematic plan view of an underside of an embodiment of a battery cover, Figure 2a schematic plan view of a top side of the battery cover opposite the bottom side Figure 1 , Figure 3 a perspective cutaway partial view of the battery cover from the Figures 1 and 2 according to section line III-III in Figure 2 , Figure 4 a detailed view of area IV of the battery cover Figure 3 in cross-section, Figure 5 a schematic plan view of an embodiment of a stamping tool and an embodiment of a hold-down arrangement in an axial direction, Figure 6 a schematic sectional partial view of the punch tool and the blank holder arrangement from Figure 4 along a plane parallel to the axial direction according to the section line VV in Figure 4 and a schematic sectional view of a die tool of the forming tool, Figure 7 the forming tool according to the examples from the Figures 4 and 5in a perspective cut partial view, Figure 8 a schematic sectional view of a battery cover provided with a bead and a notching tool for forming a notch in the bead of the battery cover, Figure 9 a schematic partial representation of the battery cover in area IX in Figure 8 with a notch in the bead in a cross-section, Figure 10 a schematic plan view of the bead in an embodiment of the battery cover in which two notches were formed in the area of ​​the bead, Figure 11 a schematic side view of an embodiment of a notching tool and Figure 12 a perspective sectional view of the notching tool from Figure 11 according to section line XII-XII.

[0030] In the Figures 1-3An embodiment of a battery cover 10 is illustrated. The battery cover 10 serves to close an opening of a battery cell housing, for example, a prismatic battery cell housing. In the illustrated embodiment, the battery cover 10 has a substantially rectangular contour, with the corner regions rounded with a radius. In the position of use of the battery cell housing, the battery cover 10 can be arranged in any position and orientation. It can close an opening in the battery cell housing that is arranged at the top, bottom, or side.

[0031] The battery cover 10 according to the Figures 1-4 was formed using a forming device 11 ( Figures 5 and 6 ) by a forming process. The battery cover 10 has a top side 12 ( Fig. 2 ) and a bottom side 13 opposite the top side 12 ( Fig. 1). By means of the forming tool 11 or the forming method according to the present invention, a predetermined overpressure breaking point 14 is produced by forming at one point in the battery cover 10. At the predetermined overpressure breaking point 14, the battery cover 10 has a minimum wall thickness w that is reduced compared to the rest of the wall thickness. For this purpose, a groove-shaped bead 15, open towards the top side 12 of the battery cover 10, is introduced into the battery cover 10 by a forming method. In the exemplary embodiment, the bead 15 is arranged in the center of the top side 12 of the battery cover 10, but could alternatively be located at any other location. The bead 15 is preferably completely closed in the manner of a ring and surrounds a central region 16. The bead 15 has a bead base 17 and two opposing bead flanks 18.In the exemplary embodiment, the bead flanks 18 are not arranged parallel to one another, but are inclined relative to a center plane M which runs centrally through the cross section of the bead, for example by approximately 3 degrees (. Fig. 4 ). This widens the bead 15 toward the top 12. Perpendicular to the center plane M, the bead 15 has a width that is smallest at the bead base 17. The width at the bead base 17 is approximately 1 mm.

[0032] The minimum wall thickness w of the battery cover 10 below the bead base 17 is, for example, less than 0.5 mm and can be approximately 0.2 mm.

[0033] On the underside 13, the battery cover 10 has a formation 19. The formation 19 has a course in the circumferential direction around the axis A corresponding to the bead 15 and is, for example, closed in a ring shape. At right angles to the center plane M, the formation 19 has a width that is greater than the width of the bead 15 and, for example, greater by a factor of 3, 4, or 5 than the width of the bead 15 at the bead base 17. In the exemplary embodiment, the formation 19 has a width of approximately 5 mm. It is formed symmetrically to the center plane M. Viewed parallel to the center plane M and at right angles to the underside 13, the formation 19 has a height h relative to the adjacent region of the underside 13 that is greater than the minimum wall thickness w of the battery cover 10, so that the bead 15 extends into the formation 19 in the region of the bead base 17.The height of the recess 19 can, for example, be at least twice the minimum wall thickness w of the battery cover and is 0.5 mm in the exemplary embodiment. Outside the recess 19, the wall thickness of the battery cover, i.e., the shortest distance between the top side 12 and the bottom side 13, is approximately 2 mm. The recess has a surface section 20 that extends parallel to the remaining bottom side 13 of the battery cover 10, offset by the height h.

[0034] In the Figures 5-7 the forming tool 11 or parts thereof is illustrated, by means of which the Figures 1-4illustrated and explained above, can be formed to form the overpressure predetermined breaking point 14. The forming tool 11 has for this purpose a punch tool 23, a die tool 24 and, in the exemplary embodiment, a hold-down arrangement 25 with an inner hold-down device 26 and an outer hold-down device 27. The battery cover 10 can be inserted between the punch tool 23 and the die tool 24, as shown schematically in Figure 7 is illustrated. By the interaction of the punch tool 23 and the die tool 24, the battery cover 10 can be deformed to form the overpressure predetermined breaking point 14.

[0035] For example, no machining or material removal of the battery cover 10 takes place during the formation of the overpressure break point 14. The overpressure break point 14 is created exclusively by forming.

[0036] The punch tool 23 has, on its side facing the die tool 24, a punch base surface 31 which, in the exemplary embodiment, is arranged in a plane running at right angles to an axis A. The direction parallel to the axis A is referred to as the axial direction R. During forming, the punch tool 23 and the die tool 24 are moved towards one another in the axial direction R in order to form the battery cover 10 arranged therebetween. The forming tool 11 can be used, for example, as a press tool in a press. For example, the die tool 24 can be arranged immovably relative to the press frame of the press, while the punch tool 23 and, in the exemplary embodiment, the hold-down assembly 25 are movable relative to the die tool 24 in the axial direction R, for which the press has at least one and, in the exemplary embodiment, exactly one drive.For example, the inner hold-down device 26 and the outer hold-down device 27 are mounted on the punch tool 23 so as to be movable in the axial direction R and can each be supported on the punch tool 23 via a spring device. The spring device determines the hold-down force with which the inner hold-down device 26 and the outer hold-down device 27 apply to the battery cover 10 during forming with the punch tool 23.

[0037] In the exemplary embodiment, the stamping tool 23 is designed in a closed ring shape and encloses the axis A. The axis A runs through the geometric center of the stamping tool 23.

[0038] A stamp part 32 extends away from the stamp base surface 31 in the axial direction R to a free end 33. In the exemplary embodiment, the stamp part 32 is designed as a ring that is completely closed around the axis A. In an alternative exemplary embodiment (not shown), the stamp part 32 could also have one or more stamp part sections that only extend in a circumferential angular range around the axis A. With such a configuration of the stamp part 32, for example, a bead 15 can be formed in the battery cover 10 that does not extend completely closed around the central region 16, but has one or more interruptions in which the wall thickness of the battery cover is greater than the minimum wall thickness w.

[0039] The die tool 24 has a support surface 37 for placing the battery cover 10 to be formed. The support surface 37 extends at least in sections at right angles to the axial direction R. The shape of the support surface 37 depends on the cross-sectional shape of the battery cover 10 to be produced. In the exemplary embodiment, the support surface 37 has at least one section that is oriented at right angles to the axial direction R and in which a forming recess 38 is present. The forming recess 38 is groove-like and has a profile in the circumferential direction around the axis A that corresponds to the profile in the circumferential direction around the axis A of the punch part 32. In the exemplary embodiment, the forming recess 38 is closed in a ring shape around the axis A.

[0040] The shape of the forming recess 38 and the punch part 32 can be straight in sections and / or curved in sections. In the embodiment of the forming tool 11 illustrated here, the shape around the axis A is rectangular with rounded corner areas, as is exemplified for the punch part 32 in Figure 5 is illustrated.

[0041] The forming recess 38 is open towards the punch tool 23 and has a recess base 39 opposite the punch part 32 in the axial direction R. The recess base 39 is, for example, flat and extends in a plane perpendicular to the axial direction R. As a modification, the recess base 39 could also have one or more elevations and / or depressions. Figure 6 Two elevations 40 are schematically illustrated by dashed lines, which represent an alternative course of the depression base 39.

[0042] Adjacent to the recess base 39, at right angles to the axial direction R, is an inner recess flank 41 on one side and an outer recess flank 42 on the opposite side. The inner recess flank 41 and the outer recess flank 42 connect the recess base 39 to the adjacent edge of the support surface 37. At right angles to the axial direction R, the shortest distance between the inner recess flank 41 and the outer recess flank 42 defines a first width b1. In the axial direction R, the distance and in particular the maximum distance between the support surface 37 and the recess base 39 defines a first depth t1.

[0043] The distance between the punch base surface 31 and the free end 33 of the punch part 32 in the axial direction R defines a second depth t2. The second depth t2 is greater than the first depth t1. In the exemplary embodiment, the second depth t2 is at least three times greater or at least four times greater than the first depth t1. For example, the second depth t2 is approximately 2.3 mm, and the first depth t1 is approximately 0.5 mm.

[0044] The punch part 32 has an annular part inner surface 34 which surrounds the axis A in the circumferential direction and an annular part outer surface 35 which surrounds the axis A in the circumferential direction. The annular part inner surface 34 and the annular part outer surface 35 are arranged at a distance from one another at right angles to the axial direction R and each connect the punch base surface 31 to the free end 33 of the punch part 32. The maximum distance between the annular part inner surface 34 and the annular part outer surface 35 defines a second width b2. The second width b2 is smaller than the first width b1. For example, the first width b1 is at least three times or at least four times or at least five times greater than the second width b2. In one embodiment, the first width b1 is approximately 5 mm and the second width b2 is 1 mm to 1.2 mm.

[0045] The hold-down device 25 is designed to generate a clamping force before and / or during the forming of the battery cover 10, which clamps the battery cover 10 between the hold-down device 25 and the die tool 24. For this purpose, the hold-down device 25 can be driven independently of the punch tool 23. The inner hold-down device 26 is enclosed by the annular punch tool 23 in a circumferential direction about the axis A. The outer hold-down device 27, in turn, completely encloses the annular punch tool 23 in the circumferential direction about the axis A. Figure 7 A quarter of the forming tool 11 is shown in perspective. The connecting edge between the two cutting planes in Figure 7 extends along axis A.

[0046] The clamping surface 46 of the hold-down device arrangement 25 facing the die tool 24, which is present in sections on the inner hold-down device 26 and on the outer hold-down device 27, extends in the exemplary embodiment in a plane that is oriented at right angles to the axial direction R. The design of the clamping surface 46 is adapted to the shape of the upper side 12 of the battery cover 10 to be formed and can also have a different shape.

[0047] Using the forming tool 11, the battery cover 10 is formed by a forming process that proceeds as follows: First, the battery cover 10 to be formed is placed on the die tool 24. The underside 13 of the battery cover 10 rests on the support surface 37 of the die tool 24. The forming recess 38 is completely or at least substantially exposed. In its formed state, the battery cover 10, for example, does not engage the forming recess 38 of the die tool 24.

[0048] By means of the hold-down device 25, the battery cover 10 to be formed is then clamped between the clamping surface 46 and the die tool 24 and subjected to a defined clamping force during the forming process. This allows the material flow during forming to be defined and undesired deformation of the battery cover 10 to be avoided. To form the battery cover 10, the punch part 32 of the punch tool is pressed against the upper side 12 and pressed into the battery cover 10, so that a bead 15 corresponding to the shape of the punch part 32 is created in the battery cover 10 by forming. The material of the battery cover 10 displaced in this process flows into the forming recess 38 of the die tool. The forming process thus forms the bead 15 and the recess 19 on the underside 13 of the battery cover 10. The shape of the formation 19 corresponds to the shape of the forming recess 38 in the die tool 24.

[0049] During the forming of the battery cover 10, the punch tool 23 is brought close to the die tool 24 to such an extent that a distance remains between the free end 33 and the forming recess 38 that corresponds to the minimum wall thickness w of the battery cover adjacent to the bead base 17. In this way, the overpressure predetermined breaking point 14 is formed on the battery cover 10.

[0050] After the bead 15 has been introduced into the battery cover 10, in a further process step, at least one notch 50 is formed in the region of the bead 15 in the battery cover 10. The at least one notch 50 is formed using a notching tool 51. The notching tool 51 has a tool part 52 for each notch 50 to be formed. In cross-section, the tool part 52 tapers toward its free end, for example, in a V-shape, triangular shape, wedge-shape, or the like. The flanks of this tool part 52 can be straight or curved when viewed in cross-section.

[0051] To form the at least one notch 50, the notching tool 51 is inserted into the bead 15 from the open side and pressed against the battery cover 10 in a transition region between the bead base 17 and an adjacent bead flank 18, so that material is displaced and the at least one notch 50 is formed. The material can be displaced into the bead 15 adjacent to the at least one notch 50. When forming the at least one notch 50, the battery cover 10 preferably rests on a support 53, so that the underside of the battery cover 13 remains undeformed during the formation of the at least one notch 50. The support 53 can be adapted to the contour of the underside 13 of the previously formed battery cover 10 ( Figure 8 ).

[0052] The at least one notch 50 introduced into the battery cover 10 within the bead 15 by means of the notching tool 51 is shown in a highly schematic cross-section in Figure 9, wherein the Figure 9 shows the area IX from Figure 8 enlarged. The notch 50 is preferably arranged outside the center plane M. The at least one notch 50 is formed in the battery cover 10 in particular in a region of the bead 15 in which the inner surface of the bead 15 curves, for example in the transition region between the bead base 17 and an adjacent bead flank 18. High stresses occur there in the event of overpressure in the battery cell housing, so that the bursting of the battery cover 10 can be set very precisely to an overpressure limit value.

[0053] Out of Figure 9It also follows that the remaining wall thickness directly below the bead 50 corresponds to a minimum wall thickness wmin. The minimum wall thickness wmin is the shortest distance between the underside 13 of the battery cover 10 and the at least one notch 50.

[0054] Depending on the shape of the at least one tool part 52, the notch 50 has, for example, a triangular or wedge-shaped configuration. It can taper from the interior of the bead 15 toward the underside of the battery cover 13.

[0055] The minimum wall thickness wmin can very precisely specify the bursting pressure for the battery cell housing. Compared to forming the bead 15, forming the at least one notch 50 displaces much less material from the battery cover 10, in particular a maximum of 10%, a maximum of 5%, or a maximum of 2% of the material volume displaced during the forming of the bead 15. As a result, elastic stresses or deformations in the notching tool 51 and the battery cover 10 during the forming of the at least one notch 50 are very small, and the specified minimum wall thickness wmin can be achieved very precisely. This allows the specified bursting pressure of the battery cell housing or the battery cover 10 to be set very precisely.In contrast, the wall thickness w below the bead base 17 after the first process step (forming the bead) may be subject to certain fluctuations due to the elasticities in the forming device 11 and the battery cover 10, so that the bursting pressure cannot be adjusted precisely enough with correspondingly small tolerance ranges for the bursting pressure. Such a more precise adjustment can be achieved by the two-stage process, in which the bead 15 is first formed and then the at least one notch 50 is introduced within the bead 15.

[0056] The at least one notch 50 is not completely closed in a ring shape in the circumferential direction or extension direction of the bead 15 - in a plan view of the upper side 12 of the battery cover 10. In contrast, in the exemplary embodiment, the bead 15 is completely ring-shaped or ring-like ( Figures 2 and 10 ). In Figure 10It is illustrated that, in one exemplary embodiment, a notch 50 is present at least in the regions in which the bead 15 extends curvedly around the central region 16 in a plan view of the top side 12 of the battery cover 10 (notches 50 are shown in dashed lines). A notch 50 can be assigned to each region of the bead 15 extending curvedly in this way. It is also possible to assign a common notch 50 to several sections of the bead 15 extending curvedly in this way, as is the case, for example, in Figure 10 There are two notches 50, each associated with two curved sections of the bead 15.

[0057] It is understood that, in a modification of the described and illustrated embodiment, the number of notches 50 may also be larger or smaller.

[0058] As in Figure 10As schematically illustrated, in the embodiment of the battery cover 10 shown here, two U-shaped notches 50 are formed into the bead 15. Accordingly, a notching tool 51 can have two U-shaped tool parts 52, as shown in the Figures 11 and 12 is shown schematically. The design of the tool parts 52 of the notching tool 51 depends on the number and course of the notches 50 to be formed and can also be designed differently in other embodiments.

[0059] The invention relates to a forming tool 11 and a forming method for producing a predetermined overpressure breaking point 14 in a battery cover 10, wherein the predetermined overpressure breaking point 14 is created in particular exclusively by forming. The forming tool 11 has a punch tool 23, a die tool 24, and optionally a hold-down device 25. On the die tool 24, there is a support surface 37 for the battery cover 10 to be formed, opposite which a forming recess 38 is formed recessed in the die tool 24. On the punch tool 23, there is a punch part 32 and, for example, an annular punch part, the cross-section of which corresponds to a bead 15 to be produced in the battery cover 10. During the forming of the battery cover 10, the punch part 32 is pressed into the battery cover 10, whereby material from the battery cover 10 flows into the forming recess 38.The punch part 32 is brought closer to the forming recess 38 in such a way that the remaining distance corresponds to a minimum wall thickness w at the overpressure predetermined breaking point 14. List of reference symbols:

[0060] 10Battery cover 11Forming device 12Top of the battery cover 13Battery cover bottom 14Overpressure break point 15Bead 16Central area 17Bead base 18Bead flanks 19Forming 20Surface section of the forming 23Punch tool 24Die tool 25Blank holder arrangement 26Inner blank holder 27Outer blank holder 31Punch base area 32Punch part 33Free end 34Ring part inner surface 35Ring part outer surface 37Support surface 38Forming recess 39Recess base 40Elevation 41Recess inner flank 42Recess outer flank 46Clamping surface 50Notch 51Notching tool 52Tool part 53Support A axis b1 first width b2 second width h height of the formation M center plane RAxial direction t1 first depth t2 second depth w minimum wall thickness

Claims

1. Forming tool for producing an overpressure predetermined breaking point (14) in a battery cover (10) for a battery cell housing, the forming tool comprising: a die tool (24) which has a forming cavity (38) in a support surface (37), wherein the forming cavity (38) extends around an axis (A) and has a cavity bottom (39), wherein the distance between the support surface (37) and the cavity bottom (39) defines a first depth (t1) in an axial direction (R) parallel to the axis (A), wherein a cavity inner flank (41) adjoins the cavity bottom (39) at right angle to the axial direction (R) on an inner side of the forming cavity (38) and a cavity outer flank (42) adjoins the cavity bottom (39) on an outer side of the forming cavity (38) opposite the inner side, wherein the shortest distance between the cavity inner flank (41) and the cavity outer flank (42) at right angle to the axial direction (R) defines a first width (b1), a stamping tool (23) which has a stamping part (32) on its side facing the die tool (24), which extends in the axial direction (R) from a stamping base area (31) to a free end (32), wherein the distance between the free end (33) of the stamping part (32) and the stamping base area (31) defines a second depth (t2), wherein the stamping part (32) is positioned in the axial direction (R) above the cavity bottom (39) and corresponds in cross-section to a bead (15) of the overpressure predetermined breaking point (14) to be formed in the battery cover (10), wherein the stamping part (32) has a ring part inner surface (34) extending between the free end (33) and the stamping base area (31) and a ring part outer surface (35) extending between the free end (33) and the stamping base area (31), which are arranged at a distance from one another at right angles to the axial direction (R), wherein the distance between the ring part inner surface (34) and the ring part outer surface (35) defines a second width (b2), characterized in that the second depth (t2) is larger than the first depth (t1), the first width (b1) is at least a factor of 2 larger than the second width (b2), and the forming tool comprises a notching tool (51) arranged to form at least one notch (50) inside the bead (15).

2. Forming tool according to claim 1, characterized in that the first width (b1) is at least the factor of 3 or 4 larger than the second width (b2).

3. Forming tool according to anyone of the preceding claims, characterized in that a hold-down arrangement (25) is provided which is arranged opposite the die tool (24) and adjacent to the stamping tool (23).

4. Forming tool according to claim 3, characterized in that the hold-down arrangement (25) comprises an inner hold-down part (26) extending along the axis (A) and into the ring-shaped stamping tool (23) and an outer hold-down part (27) surrounding the stamping tool (23) .

5. Forming method for producing an overpressure predetermined breaking point (14) in a battery cover (10) for a battery cell housing using the forming tool (11) according to anyone of the preceding claims, comprising the following steps: - positioning a battery cover (10) to be deformed on the die tool (24) such that its bottom side (13) rests on the support surface (37) of the die tool (24) and the forming cavity (38) of the die tool (24) remains free, - pressing the stamping part (32) of the stamping tool (23) into the battery cover (10), whereby material of the battery cover (10) is displaced into the forming cavity (38) of the die tool (24) and a bead (15) is created which is open to a top side (12) of the battery cover (10), such that a wall thickness (w) of the battery cover (10) below the bead (15) is smaller than the wall thickness at other locations of the battery cover (10) and thus forms the overpressure predetermined breaking point (14), - forming at least one notch (50) inside the bead (15) by means of a notching tool (51).

6. Forming method according to claim 5, characterized in that the battery cover (10) is clamped between a hold-down arrangement (25) and the support surface (37) of the die tool (24) prior to or concurrently with the pressing of the stamping tool (23) into the battery cover (10).

7. Forming method according to claim 5 or 6, characterized in that the wall thickness of the battery cover (10) below the notch (50) has a minimum wall thickness (wmin).

8. Forming method according to anyone of the claims 5 to 7, characterized in that the at least one notch (50) is not closed in a ring shape in the circumferential direction.

9. Forming method according to anyone of the claims 5 to 8, characterized in that the notch (50) is formed in a transition region between a bead bottom (17) and a bead flank (18).